Technical Paper

Do you have the right steel for this sour service pipeline?

Microalloyed Steels for Sour Service International Seminar

Hydrogen-induced cracking (HIC), a type of pipeline failure that can occur under sour service conditions, is usually caused by hydrogen atoms that diffuse into steel and recombine at traps (such as elongated inclusions), causing microscopic blisters to form, which subsequently link and propagate. Neither residual nor applied stressis required for HIC to occur. Cracks are usually parallel to the rolling plane. To quantify susceptibility of linepipe steels to HIC and for predicting resistance to HIC in service, two parameters were defined: threshold hydrogen concentration in the steel and threshold pH in the environment. The threshold hydrogen concentration is the diffusible hydrogen concentration in the steel above which the steel cracks within the maximum test duration of 96 hours. The threshold pH is the pH in the environment below which the steel cracks within 96 hours,a test duration specified in the ANSI/NACE Standard TM0284.The study was carried out using unstressed coupons immersed in acidified, buff red, de-aerated saline solutions of pH between 1.1 and 5.9, saturated with H2S. Quantitative relationships between susceptibility to HIC and steel composition, particularly the inclusion content, were explored. The relative susceptibility of a steel to HIC can be estimated by characterizing the inclusion content.(AU) © CBMM
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